The Leonardo, Sandton

Completed in 2019, The Leonardo rises 234 metres over Sandton and is the tallest building in Africa. The mixed-use tower combines luxury residential apartments, hotel and commercial space, with extensively landscaped terraces stepping up the structure.

Height changes the physics of waterproofing. Wind-driven rain at 200m does not fall onto surfaces so much as it is driven horizontally into them, loading junctions and upstands in ways that ground-level detailing never anticipates, and wind uplift becomes a genuine design factor for the membrane system. The planted terraces that give a building like this its character are among the most demanding details in the discipline: waterproofing beneath soil and irrigation must resist permanent moisture and root penetration, and it sits directly above occupied luxury interiors. Below ground, multi-level basements must hold back water under hydrostatic pressure. In every one of these locations the membrane is permanently buried — remedial access after handover is close to prohibitive, so the installation has to be right first time.